SEATTLE - Washington state's top polluter isn't a pulp mill, a power plant or refinery. It's the newly awakened Mount St. Helens.

Since the volcano began erupting in early October, it has been pumping out 50 to 250 tons a day of sulfur dioxide, the lung-stinging gas that causes acid rain and contributes to haze. At peak, that's more than double the amount from all the state's industries combined.

Normally, the state's No. 1 polluter is a coal-fired power plant owned by the Canadian firm TransAlta. The plant churned out 200 tons a day of sulfur dioxide until regulators demanded $250 million worth of renovations, bringing the level down to 27 tons a day.

Tough to get those kind of results from a volcano.

"You can't put a cork in it," said Greg Nothstein of the Washington Energy Policy Office.

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Because the area around St. Helens is so sparsely populated, officials say they haven't heard complaints about respiratory problems linked to the emissions. But people with breathing ailments probably would feel the effects if they lived close to it, said Bob Elliott, executive director of the Southwest Clean Air Agency.

"We are very fortunate, in terms of the impact on human health, that Mount St. Helens is pretty remote," Elliott said.

Worldwide, sulfur dioxide emissions from volcanoes add up to about 15 million tons a year, compared to the 200 million tons produced by power plants and other human activities.